1. Field of the Invention
The present invention relates to a compressor.
2. Description of the Related Art
A type of compressor is disclosed, for example, in the Patent brochure of Japanese Utility Model Application, Laid-Open No. Sho. 62-84681. This type of compressor is configured to have: a cylinder block including a center through-hole and cylinder bores provided around the center through-hole; a valve plate which is jointed to a top-dead-center-side surface of the cylinder block, and which includes intake holes and exhaust holes; a rear head which is jointed to the cylinder block with the valve plate being interposed in between, and in which an intake chamber and an exhaust chamber both communicating with the cylinder bores are formed; a front head in which a crank chamber is formed, the crank chamber jointed to bottom-dead-center-side surfaces of the respective cylinder bores to communicate with the cylinder bores; pistons arranged in the respective cylinder bores to be reciprocatable therein; a driving shaft which is pivotally supported by the center through-hole in the cylinder block with a radial bearing and a thrust bearing being interposed in between, and which is rotatable in the crank chamber; and a conversion mechanism for converting rotations of the driving shaft to reciprocating motions of the respective pistons.
In this type of compressor, the pistons reciprocate back and forth in response to the rotation of the driving shaft. Thereby, a compressed medium is taken from the intake chamber into the cylinder bores, and is compressed there. The compressed medium thus compressed is discharged from the cylinder bores to the exhaust chamber. During the compression process carried out by the pistons, the compressed medium thus compressed to a high pressure (or a blow-by gas) flows into the crank chamber from the gap between the slide surfaces of each set of the cylinder bore and the piston. For the purpose of discharging the high-pressure compressed medium which flows into the crank chamber, an air supply passage for allowing the crank chamber and the intake chamber to communicate with each other is provided in the compressor. The high-pressure compressed medium in the crank chamber is fed back to the intake chamber through this air supply passage. In general, oil is retained in the crank chamber. This oil is splashed up into mist by the conversion mechanism located in the crank chamber, and the oil mist is supplied to the sliding members in the crank chamber. Part of the oil mist inevitably flows out of the crank chamber while accompanied by the compressed medium which flows out from the crank chamber to the intake chamber through the air supply passage. It is desirable, however, to keep the oil mist inside the crank chamber where the chief sliding members are located.
In the case of the current technology, for the purpose of retaining the oil mist inside the crank chamber, a part of the air supply passage is provided in the driving shaft and has an inlet at a portion of the outer peripheral surface of the driving shaft, which portion faces the crank chamber. As a result, when the oil mist in the crank chamber is going into the inlet of the air supply passage, the oil mist is pushed back to the crank chamber due to the centrifugal action of the driving shaft. Thereby, it is possible to retain much of the oil inside the crank chamber.
However, the compressed medium which flows from the crank chamber to the intake chamber tends not to flow to the center through-hole in the cylinder block. This makes it likely to supply only an insufficient amount of oil to the thrust bearing and the radial bearing which are interposed between the center through-hole in the cylinder block and the driving shaft.
Particularly in a structure in which the radial bearing is a slide bearing, there is no interstice in the bearing. For this reason, only an extremely small amount of compressed medium passes through the radial bearing. As a result, the radial bearing may run out of supplied oil.